So we spent a full week in the high desert in California and the temps were in the 20's to 40's day and night. 4" of snow. The new set up I revamped by adding an additional 150w panel, to make 450w. Running #4 conductor down to the new controller location near the battery bank(4 each 6v GC) worked out great. Able to run the furnace at night to keep the frosties away and charge during the day. And the days weren't all sunny either......Each night after the surface charge fluffed off I had 12.8 volts.